Android Facebook 登录按钮空指针异常 fragment

Question

当我尝试使用适用于 Android 的 Facebook SDK 通过 facebook 登录时出现此错误。我无法在 fragment 中添加 Login via Facebook button，这是我在预览中遇到的错误。预览显示 Rendering Problems，当我点击 Show exception 时，这就是我所看到的。

java.lang.NoClassDefFoundError: Could not initialize class com.facebook.login.widget.LoginButton
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.jetbrains.android.uipreview.ViewLoader.createNewInstance(ViewLoader.java:413)
at org.jetbrains.android.uipreview.ViewLoader.loadView(ViewLoader.java:105)
at com.android.tools.idea.rendering.LayoutlibCallback.loadView(LayoutlibCallback.java:176)
at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:207)
at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:132)
at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:806)
at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:64)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:782)
at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
at android.view.LayoutInflater.inflate(LayoutInflater.java:385)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:400)
at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:332)
at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:350)
at com.android.tools.idea.rendering.RenderService$5.compute(RenderService.java:708)
at com.android.tools.idea.rendering.RenderService$5.compute(RenderService.java:697)
at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:932)
at com.android.tools.idea.rendering.RenderService.createRenderSession(RenderService.java:697)
at com.android.tools.idea.rendering.RenderService.render(RenderService.java:816)
at org.jetbrains.android.uipreview.AndroidLayoutPreviewToolWindowManager.doRender(AndroidLayoutPreviewToolWindowManager.java:646)
at org.jetbrains.android.uipreview.AndroidLayoutPreviewToolWindowManager.access$1700(AndroidLayoutPreviewToolWindowManager.java:82)
at org.jetbrains.android.uipreview.AndroidLayoutPreviewToolWindowManager$7$1.run(AndroidLayoutPreviewToolWindowManager.java:589)
at com.intellij.openapi.progress.impl.ProgressManagerImpl$2.run(ProgressManagerImpl.java:178)
at com.intellij.openapi.progress.ProgressManager.executeProcessUnderProgress(ProgressManager.java:209)
at com.intellij.openapi.progress.impl.ProgressManagerImpl.executeProcessUnderProgress(ProgressManagerImpl.java:212)
at com.intellij.openapi.progress.impl.ProgressManagerImpl.runProcess(ProgressManagerImpl.java:171)
at org.jetbrains.android.uipreview.AndroidLayoutPreviewToolWindowManager$7.run(AndroidLayoutPreviewToolWindowManager.java:584)
at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:320)
at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:310)
at com.intellij.util.ui.update.MergingUpdateQueue$2.run(MergingUpdateQueue.java:254)
at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:269)
at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:227)
at com.intellij.util.ui.update.MergingUpdateQueue.run(MergingUpdateQueue.java:217)
at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
at com.intellij.util.Alarm$Request$1.run(Alarm.java:327)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:695)

当我运行应用程序时，我尝试在 onViewCreated 方法中创建的 LoginButton 实例出现空指针异常

    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    FacebookSdk.sdkInitialize(getActivity().getApplicationContext());
    mCallbackManager=CallbackManager.Factory.create();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_main, container, false);


    return view;
}

 @Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    LoginButton loginButton = (LoginButton)view.findViewById(R.id.login_button);
    loginButton.setReadPermissions("user_friends");
    loginButton.setFragment(this);
    loginButton.registerCallback(mCallbackManager,mCallback);
    mTextDetails = (TextView) view.findViewById(R.id.text_details);
}

   @Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    mCallbackManager.onActivityResult(requestCode, resultCode, data);
}

我尝试按照这个问题中的建议进行操作 - Could not initialize LoginButton Facebook-sdk for android , 但没有骰子。

有什么想法吗？

编辑:

我将 LoginButton 实例化移动到 OnCreateView 但仍然遇到相同的错误。

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_main, container, false);
    LoginButton loginButton = (LoginButton)view.findViewById(R.id.login_button);
    loginButton.setReadPermissions("user_friends");
    loginButton.setFragment(this);
    loginButton.registerCallback(mCallbackManager,mCallback);
    mTextDetails = (TextView) view.findViewById(R.id.text_details);


    return view;
}

编辑 2:

这是我的 xml 文件:

fragment_login.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment">

<TextView
    android:id="@+id/text_details"
    android:gravity="center"
    android:layout_above="@+id/login_button"
    android:text="@string/hello_world"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

<com.facebook.login.widget.LoginButton
    android:id="@+id/login_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:layout_centerInParent="true" />

还有我的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme">
    <meta-data
        android:name="com.facebook.sdk.ApplicationId"
        android:value="@string/facebook_app_id" />

    <activity
        android:name=".MainActivity"
        android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name="com.facebook.FacebookActivity"
        android:configChanges="keyboard|keyboardHidden|screenLayout|screenSize|orientation"
        android:theme="@android:style/Theme.Translucent.NoTitleBar"
        android:label="@string/app_name" />
</application>

Answer 1

您使用的 fragment xml 错误。它是 fragment_login 但在代码中它是 R.layout.fragment_main